1. Field of the Invention
The present invention relates to a semiconductor device having an electrode with a layered structure of polysilicon and metal or metal silicide, for instance, an electrode made of polycide.
2. Description of the Related Art
In recent years, with the purpose of satisfying demands that elements should have still higher speed, the metal such as tungsten and the metal silicide such as tungsten silicide have become being utilized as an electrode material. For instance, an electrode made of polycide that is structurally layers of polysilicon and silicide is in wide use.
FIG. 3 shows a conventional method of manufacturing a portion around an emitter electrode for a bipolar transistor. First, field oxide films 101 each of which is to serve as an element isolation region are formed, on a semiconductor substrate 1, to a thickness of 500 nm or so. Then, an N+-buried collector region 2, an Nxe2x88x92-collector region 3, an N+-collector region 4 and a P-base region 5 are formed, in succession, each by performing the ion implantation through a mask formed from the resist using the method of photolithography (FIG. 3(a)). Next, as shown in FIG. 3(b), an insulating film 102 is formed, and by means of photolithography a region which is to be an emitter electrode section is patterned thereon, and an opening is made therethrough by plasma etching using the photoresist as a mask, and thereafter a polysilicon film 103 is grown to a thickness of 150 nm or so. Next, arsenic is ion-implanted into the polysilicon film 103 and a subsequent heat treatment diffuses the arsenic into the silicon substrate, forming an N+-emitter region 6. If the polysilicon film 103 is exposed to the air at this point, a natural oxidation film 104 is brought to grow on the surface of polysilicon, as shown in FIG. 3(c).
Further, after a tungsten silicide film 105 is formed over the polysilicon film 103, the plasma etching is selectively applied thereto through a mask of the photoresist and thereby a polycide emitter electrode is formed (FIG. 4). Subsequently, electrodes are formed in a base, a collector and an emitter region, respectively, by the conventional techniques, which accomplishes a bipolar transistor.
The emitter electrode of the bipolar transistor manufactured by the above-mentioned prior art, however, has a natural oxidation film lying between the polysilicon film 103 and the tungsten silicide film 105, as shown in FIG. 4. This gives rise to a problem that the value of resistance for the emitter electrode thereof becomes high, for the natural oxidation film has high resistance.
Accordingly, an object of the present invention is, in an electrode with a layered structure of polysilicon and metal or metal silicide, for instance, an electrode made of polycide, to remove a high-resistance layer such as a natural oxidation film and lower the value of resistance for the electrode.
In light of the above problem, the present invention provides a method of manufacturing a semiconductor device; which comprises the steps of:
(a) forming an insulating film on the surface of a silicon substrate, and thereafter forming a polysilicon film over said insulating film;
(b) applying the plasma etching to the surface of said polysilicon film, using the inert gas;
(c) forming a metal film over said polysilicon film; and
(d) patterning said metal film and polysilicon film, and thereby forming an electrode.
In the manufacturing method of a semiconductor device according to the present invention, when an electrode with a layered structure of polysilicon and metal or metal silicide, for instance, an electrode made of polycide, is formed, a polysilicon film is first formed and thereafter the plasma etching is applied to the surface thereof, using the inert gas. Consequently, such a high-resistance layer formed over the surface of the polysilicon film as the natural oxidation film is removed. In an electrode made of polycide or the like, because a current flows along a direction perpendicular to the layered structure, the state of the interface between the polysilicon and the metal film (silicide or the like) strongly affects the value of resistance for the electrode. Therefore, the above-mentioned removal of the high-resistance layer can lower the electrode resistance with effect.
In short, in the present invention, after the formation of a polysilicon film, the plasma etching with the inert gas is applied to the surface thereof so that a high-resistance layer on the surface of polysilicon can be removed, which enables to lower the value of the electrode resistance.